This invention relates to a novel continuous process for preparing metal complex pigments, especially metal complex intercalates of azobarbituric acid and its derivatives.
Unpublished German patent application 19,924,763.3 describes metal complexes of substituted azo compounds and a batch process for their preparation. In the process, azo compounds of the formula (A) 
wherein
R and Rxe2x80x2 are independently OH, NH2, NHxe2x80x94CN, acylamino, or arylamino and
R1 and R1xe2x80x2 are independently xe2x80x94OH or xe2x80x94NH2, are complexed with a metal salt of metals selected from the group consisting of Ba, Ca, Zn, Cu, Fe, Co, Sr, Cr, Sn, Al, Mg, Cd, Pb, and La and the resultant metal complex is reacted with a compound to be intercalated (i.e., the intercalate).
Inclusion compounds, intercalation compounds, and solid solutions of metal complexes are known from the literature. Such compounds and their preparation are described for example in EP 74,515 A1.
To prepare the aforementioned pigments in a batch process, first an alkali metal salt of azobarbituric acid or derivatives thereof (formula (I)) are dispersed in water and subsequently admixed with the corresponding amount of a polyvalent metal salt and a corresponding amount of the intercalate. The mixture must then be stirred at 95xc2x0 C. for several hours. The reacted mixture is finally adjusted to a pH of about 5 and the ready-prepared product is isolated.
The particular disadvantage of the aforementioned batch process is that, particularly at large vessel volumes, the mixture cannot be heated in the desired uniformity. A consequence of such temperature gradients is that mutually competing laking and intercalation reactions take place. A further disadvantage of the batch process is the appearance of an unwanted fraction of particularly finely divided products (i.e., having an average particle diameter of less than 50 nm). In pigment finishing, these products absorb a large portion of the dispersant used for the finishing and then make very little contribution to the color strength desired for the product.
The dispersion harshness of the product is usually more than 300, so that the product from a batch process must be subjected to a subsequent additional heat treatment for applications in which rapid development of color strength is needed.
A further disadvantage is that product quality fluctuates from batch to batch with regard to color, particle size, and harshness of the products. This fluctuating product quality is due to the lack of a control means in the batch process.
It is an object of the present invention to provide a process that avoids the aforementioned disadvantages of the batch process and provides consistent, fluctuationless production of the metal complex intercalates mentioned above. The process is to be continuous, with the laking of the azobarbituric acid compound with polyvalent ions taking place in a first step and the intercalation in the second step.
The invention accordingly relates to a continuous process for preparing metal complexes of polyvalent metal ions with mono-, di-, tri-, or tetraanions of an azo compound conforming to the formula (I) 
or one of its tautomeric structures,
wherein
R and Rxe2x80x2 are independently xe2x80x94OH, xe2x80x94NH2, xe2x80x94NHxe2x80x94CN, arylamino, acylamino, or p-chlorophenyl, and
R1 and R1xe2x80x2 are independently xe2x80x94OH or xe2x80x94NH2,
that intercalate at least one intercalate that is a compound different from the compounds of formula (I),
wherein the metals of the polyvalent metal ions are selected from the group consisting of Ca, Zn, Cu, Fe, Mn, Ni, Co, Sr, Ba, Cr, Sn, Al, Mg, Cd, Pb, and La,
comprising
(1) stirring an aqueous dispersion of an alkali metal salt of compounds of formula (I) with the metal salt of the polyvalent metal at a temperature of 10 to 35xc2x0 C. (especially 20 to 25xc2x0 C.), especially for a period of 1 to 25 min (preferably 5 to 20 min), if appropriate at a pH of 0.5to 5.5,
(2) admixing an aqueous solution, dispersion, or emulsion of the intercalate, if appropriate with comminution of solid particles (agglomerates) of the mixture before and/or after the admixing of the intercalate,
(3) passing the mixture through a reaction zone (such as represented by 18 in FIG. 1) at a temperature of 85 to 140xc2x0 C. (preferably 110 to 120xc2x0 C.) under pressure (preferably 105 to 4xc3x97105Pa), especially for a residence time of 1 to 15 min (preferably of 2 to 10 min) in the reaction zone, while regulating the pH of the mixture entering the reaction zone so that the product dispersion leaving the reaction zone has a pH of 0.5 to 3,
(4) adjusting the pH of the mixture to at least pH 5, and
(5) isolating the intercalated metal complex.